The velvet worm, an invertebrate belonging to the phylum Onychophora, represents a lineage of terrestrial animals dating back over 500 million years. These slow-moving creatures, often found in humid, tropical forests, capture prey using a sophisticated biological adhesive. This unique predatory strategy centers on the forceful, high-speed projection of a liquid slime that rapidly transforms into a solid, inescapable net upon contact with the target.
The Biological Machinery for Slime Production
The specialized equipment for this attack is located in the velvet worm’s head region. A pair of modified appendages, known as oral papillae, flank the creature’s mouth, serving as the twin nozzles for the adhesive. These papillae are connected internally to large slime glands, which are modified crural glands.
These internal slime glands extend far back into the body cavity, occupying a significant amount of space. The glands continuously secrete and store the adhesive material, maintaining it under high hydrostatic pressure. This internal pressure is necessary to generate the force required for the slime’s rapid ejection over a distance. The entire system functions like a natural, pressurized squirting device, ready for deployment.
The High-Speed Capture Maneuver
The velvet worm attack begins with detecting a meal, often sensed through ground vibrations or chemical cues picked up by the antennae. Once a target is located, the worm positions its body and aims its head to align the oral papillae. The actual ejection is an instantaneous, fluid-driven event.
The liquid adhesive launches from the twin papillae at velocities estimated between 3 to 5 meters per second. This rapid ejection creates a passive oscillation of the papillae, vibrating them at a frequency of 30 to 60 Hertz. This vibration is a result of the fluid’s inertia interacting with the elasticity of the papillae’s tissue, similar to an untethered garden hose.
The resulting effect is a chaotic, crisscrossing double jet of slime that weaves a dense, three-dimensional net around the prey. This sticky web can be projected up to 30 centimeters, effectively entangling and immobilizing the victim. The entire maneuver is completed in a fraction of a second, securing the prey before it can escape.
The Chemistry Behind the Sticky Slime
The capture fluid is a complex biological hydrogel composed primarily of water and specialized proteins, including leucine-rich repeat (LRR) proteins. These proteins are stored in a liquid state within the water-based solution. The material is mechano-responsive, meaning its state changes when subjected to mechanical forces.
The high shear forces experienced during ejection through the narrow papillae, combined with air exposure, trigger a rapid phase transition. The liquid material quickly self-assembles into solid, cohesive fibers that harden to a stiffness comparable to synthetic nylon. Research has identified a rare chemical modification in the slime proteins, involving phosphonate groups, which contributes to the strength and adhesive properties of the final fiber network.
The solidified net is non-toxic and water-soluble. Since the worm lives in damp habitats, the hardened slime can dissolve over time or be reabsorbed by the worm, preventing the animal from being trapped by its own hunting residue. This quick-hardening material provides a strong, temporary trap that is recycled after the meal is finished.
How the Velvet Worm Consumes Its Prey
With the prey secured within the rigid net of hardened slime, the velvet worm moves toward the victim. The worm uses mandibles, located deep within the oral cavity, to puncture the exoskeleton of the captured arthropod. This initial puncture is the entry point for the next stage of feeding.
Once the cuticle is breached, the velvet worm injects digestive saliva containing hydrolytic enzymes into the prey’s body. These enzymes break down the internal tissues, liquefying the meal while it remains externally constrained. This process is known as external digestion, a strategy used by some terrestrial predators.
The worm then uses its muscular pharynx to suck up the resulting nutrient-rich fluid, leaving behind the empty exoskeleton shell. This consumption process is slow and thorough. Some species have also been observed consuming portions of the protein-rich capture slime, suggesting it provides an additional source of nutrients.